Scissor Jack

ABSTRACT

In general, a scissor jack is described. A typical embodiment includes four arms (4) hingedly arranged to provide two opposite elbows between a base (10) and a load support (11), a pair of trunnions (2, 2.1), one at each elbow connected by a partially threaded shaft (12) with one end of the shaft rotatably engaged in the threaded trunnion (2.1) to extend beyond the outer corner of the elbow.Located on the shaft and between the outer two trunnions is an assembly comprising a pair of levers (3) pivotally assembled on a third trunnion (5) which forms the one end of a double yoke (1) comprising two rods slideably passing through the outer trunnion (2) and beyond the elbow. In contact with and operating against the inner trunnion (5) is a thrust bearing (9) fixed in portion on the shaft by means of a flange. Springs (6) are attached to individual levers and the corresponding arms for alignment purpose.Fully collapsed the angle of operation of the first stage of the lever in contact with the pivot point (8) is such that it simulates the same optimum angle of a typical scissor jack at approximately 75% of it&#39;s range. Once the first stage of the lever is fully extended the second stage takes over at pivot point (7) when it is again at the optimum angle. Once the second stage of the sever is fully extended the jack itself is in an optimum height for further lifting. Thus the jack is able to utilise the full extent of it&#39;s range of motion.

TECHNICAL FIELD

The present invention relates generally to the field of jacking systems, and more particularly to the lifting of light motor vehicles.

BACKGROUND ART

The need has long existed for an improved jack for light motor vehicles that collapses sufficiently low enough for low slung vehicles and yet has a lifting stroke greater than the suspension travel of Sport Utility Vehicles. The focus here is on the scissor jack because of it's simplicity.

Scissor jacks typically have a very limited lifting range and are only operable within the last 25% of their stroke. Fully collapsed they have no useful lifting capacity and if used at less than 75% of their full height are prone to breaking. Ideally a jack should be stable and robust. Further, it should have the ability to utilise it's full range of motion. The invention is primarily aimed at, but not limited to the automotive industry. The invention disclosed satisfies these needs to a remarkable degree.

DISCLOSURE OF THE INVENTION

In general, a pantograph type lifting apparatus commonly known as a scissor jack to raise vehicles is described. A typical embodiment comprises four arms hingedly arranged to provide two opposite elbows between a base and a load support a pair of trunnions, one at each elbow connected by a partially threaded shaft with the threaded end rotatably engaged in a threaded trunnion to extend beyond the outer corner of the elbow. The shaft further includes on the unthreaded section held in place by a flange a thrust bearing which is part of the assembly of a pair of levers which pivot about a third trunnion between the outer two trunnions, which is secured by a yoke of two rods passing slidably through the outer trunnion at the opposite elbow.

Referring to the images wherein like reference numerals designate corresponding parts throughout the several images, reference is made first to FIG. 1 and FIG. 2 that illustrates the full view of an embodiment of a scissor jack.

FIG. 3 illustrates the internal layout and assembly of the levers in relation to the jack.

In a typical embodiment, other methods in place of the threaded rod could be utilised, but not limited to, hydraulic or pneumatic cylinders.

In general, the embodiments described herein relate generally to jacking systems that can be used in a variety of sizes to lift various loads. A typical embodiment is used for light motor vehicles. It is understood that the embodiments can be modified in several ways for different uses and implementations.

With respect to the above description then, it is to be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the images and described in the specification are intended to be encompassed by the present invention. 

1. A scissor jack comprising four arms hingedly arranged to provide two opposite elbows between a base and a load support, with a pair of trunnions at the elbows connected by a partially threaded shaft, passing through a third inner trunnion which allows free rotational motion of the unthreaded section of the shaft.
 2. The jack of claim 1, wherein the inner trunnion is connected to two rods forming a yoke, the rods of which slideably pass through the trunnion of the outer elbow to extend beyond the elbow.
 3. The jack of claim 2, wherein a thrust bearing is located in a fixed position on the unthreaded section of the shaft and in is contact with the yoke.
 4. The jack of claim 2, further comprising a pair of free floating levers pivotally secured on the trunnion.
 5. A jack of claim 2, wherein the two rods are bolts or rods with nuts to prevent withdrawal from the trunnion of the outer elbow.
 6. The jack of claim 4, wherein springs or any other retaining method are attached to the levers for the purpose of alignment when the jack is or lowered. 